DESCRIPTION: The three dimensional structures of unliganded p66/p51 HIV-1 reverse transcriptase (RT), together with co-crystals containing duplex DNA and non-nucleotide-based inhibitors provide an important framework for examining how the multiple subdomains contribute to the biosynthetic and degradative functions of this key retroviral enzyme. The continuing goal of this project is application of molecular, biochemical and biophysical methodologies to provide both mechanistic and high resolution information on nucleoprotein complexes representative of specific events in the HIV replication cycle. In converting the single-stranded RNA genome of the invading virus into double-stranded pre-integrative DNA, the retroviral replication machinery must accommodate three structurally distinct nucleic acid duplexes, namely B-form duplex DNA, A-form duplex RNA and non-a, non-B RNA DNA hybrids. Recent data also indicates that unusual configurations of certain nucleic acid duplexes provides important control mechanisms for initiation and termination of (+) strand synthesis (the polypurine tract and central termination sequences, respectively). The aim of the proposed studies is to evaluate such replication complexes from the perspective of both the specific nucleic acid duplex and multi-subdomain retroviral reverse transcriptase (RT). In vitro site-directed mutagenesis of subdomains of HIV-1 and related lentiviral RTs interacting with single-stranded template overhand and double-stranded template-primer duplex will be continued, the consequences of which will be evaluated on specific nucleic acid duplexes closely mimicking events in retroviral replication. In parallel, chemical and enzymatic footprinting will be employed to provide high resolution structural data on these nucleoprotein complexes. HIV-1 RT will also be genetically engineered to accommodate nucleic acid cleaving, photoactivatable and fluorescent adducts at rationally designed positions (guided by the three dimensional structure of the HIV-1 enzyme). Such reagents permit a detailed analysis of alterations to subdomain geometry following alteration or removal of structurally important residues. This combination of methodologies will be applied to both the N-terminal DNA polymerase and C-terminal ribonuclease H domains of structurally-related lentiviral enzymes, thereby providing a comprehensive picture of subdomain architecture, offering the possibility of designing a new generation of allosteric inhibitors to impede movement of the translocating enzyme.